This invention relates to a storage controller and a control method for controlling storage devices of a computer system. More particularly, this invention relates to a storage controller which has a function to collect complete information to be dumped at the start time of a dump process even when this dump process of data records on the storage device is performed in concurrence with another job, and also relates to a method of the dump process.
In operating a computer system, in order to maintain the reliability of data records stored in the external storage device by a system-wise data integrity protection, such as by using magnetic disk units, it is generally practiced to copy, in other words, dump data records to another recording medium, like a magnetic tape.
Various techniques have been proposed aimed at decreasing the amount of records to be handled in a dump process or improving the performance of the dump process. For example, in a system revealed in JP-A-57-90770, the disk control unit records information about the location of an updated data record on the disk unit into a control memory in the disk controller. A dump program which runs on the central processing unit, before dumping the data records on the disk unit, reads information about the locations of updated data records stored in the control memory. After this, the dump program reads only updated data records from the disk unit according to the information about the locations of updated data record, and writes them on another recording medium. Under this arrangement, only updated data records are dumped by the dump process, so that the number of data records subject to the dump process can be reduced.
A system such as this has a problem that other jobs cannot be executed until a dump process is completed. The reason is that if a data record is updated during execution of another job, there is a possibility that this updating is looked over and the new data is not dumped.
As a technique for solving this problem, there is a system disclosed in JP-A-1-231150. In this system, there are two kinds of data record location information: a first identification information is used to show the locations of data records updated on the time base, and a second identification information is used to show the locations of data records updated while a dump process is in progress. Accordingly, it is possible to identify data records which are updated while a dump process is being executed, and specify those data records as being subject to the next dump process. Consequently, data records which are updated in concurrence with or in the intervals of ordinary data processing can be dumped without omission.
On the other hand, as a technique for improving the performance and the reliability of the storage system, there is a disk array system disclosed in JP-A-62-293355. In this system, a method is adopted that a plurality of parity segments are generated from a plurality of data records, and data records in a set corresponding to a parity record are stored in different storage devices, and parity records corresponding to data records of all sets are arranged such that they are not in the possession of a storage device. In a system using a control method mentioned above, when a data record is updated, the parity record, too, needs to be updated. An adopted method for updating a data record is to generate a modification mask from an old data record and a new data record, then read a parity record from the storage device, further generate a new parity record by the read-out parity record and the modification mask, and write the new parity record back to the storage device.
In JP-A-1-231150 mentioned above, because data records to be dumped are limited to updated data records, it is possible to reduce the amount of data to be handled in the dump process, and execute the dump process and another job concurrently. Therefore, the dump process can be executed in a short time without interrupting the online operations. However, in this system, as described above, complete information to be dumped at a given time cannot be collected. To be more specific, for a time from the start of the dump process until data records have been actually dumped to the processor, if an update request is made on a certain data record, the completeness of information on the data records at the start time of the dump process will lost.
Meanwhile, in the disk array system, a plurality of parity records are generated from a plurality of parity records, and the thus generated parity records are dispersed into a plurality of storage devices to ensure the reliability of data records and cut down the overhead required for the improvement of reliability. By this arrangement, the reliability can be increased against hardware faults in the storage system. However, preventive measures against operation errors of the user are not provided. Even in the disk array system such as this, the dump process is indispensable, and the same problem as in JP-A-1-231150 arises.